1. Field of the Invention
The present invention relates to an image forming apparatus. More particularly, the present invention relates to a paper reverse-feeding apparatus for an image forming apparatus.
2. Description of the Related Art
Typically, image forming apparatuses perform single-side-printing. If a double-side-printing unit is provided with such an image forming apparatus, however, the image forming apparatus can perform double-side-printing. The double-side-printing unit is separately provided with a paper feeding path within the image forming apparatus so as to resend a single-side-printed paper to a developing unit of the image forming apparatus.
FIG. 1 shows a conventional image forming apparatus capable of performing double-side-printing. The image forming apparatus capable of performing double-side-printing comprises a main body 10 forming the appearance of the image forming apparatus as shown in the FIG. 1, a paper feeding cassette 11 mounted on the bottom of the main body 10, a pick-up roller 12 for picking up a paper from the paper feeding cassette 11, a feeding roller 13 for feeding the paper picked up by the pick-up roller 12, a developing unit 14 for developing an image on the paper fed by the feeding roller 13, and a fusing unit 15 for fixing the image developed in the developing unit 14.
The image forming apparatus further comprises a paper discharge path 16, through which the paper passing through the fusing unit 15 is discharged, and a paper discharge roller 17 installed at the outlet of the discharge path 16. A paper reverse-feeding path 20 is laterally branched from the paper discharge path 16 just before the paper discharge roller 17 and extends downwardly from the paper discharge path 16. An opening and shutting plate 21 are also provided to open or shut the paper reverse-feeding path 20.
Reverse-feeding of the paper for double-side-printing is performed if the paper is discharged through the paper discharge path 16 and the paper discharge roller 17 reverses rotation before the tail edge of the paper is completely discharged by the discharge roller 17. During the reverse-feeding process, the opening and shutting plate 21 is driven to open the paper reverse-feeding path 20 as well as to shut the paper discharge path 16, and the sheets of papers fed to the reverse-feeding path 20 are transferred by a plurality of paper transfer rollers 22 and then fed by the pick-up roller 12, so that printing can be implemented on the previously non-printed sides of the papers. Sheets of paper that are being printed on both sides make a complete loop inside the image forming apparatus.
In this case, however, because the feeding of a new printing paper to the developing unit 14 is interrupted while the paper is being transferred to the reverse-feeding path 20 and fed to the developing unit, the speed of double-side-printing is remarkably reduced as compared to that of single-side-printing. Therefore, what is needed is to develop a paper reverse-feeding apparatus for an image apparatus that can increase the speed of double-side-printing. This is important to consumers of these devices because speed in the double-side-printing mode is given much weight in regard to degree of satisfaction of users, especially in the case of an office image forming apparatus or an expensive color image forming apparatus requiring high speed printing operation.